Inverted loud speaker



March 6, 1962 Filed May 19, 1960 W. E. SEE

INVERTED LOUD SPEAKER 2 Sheets-Sheet 1 INVENTOR.

ATTORNEY March 6, 1962 w. E. SEE

INVERTED LOUD SPEAKER 2 Sheets-Sheet 2 Filed May 19, 19 0 I l I 1 x INVENT OR. B %/Z /':.5e"e

ATTOQ/VEK 3,024,323 Patented Mar. 6, 1962 3,024,323 INVERTED LOUDSPEAKER Walter E. See, Peru, Ind., assignor to General MotorsCorporation, Detroit, Mich, a corporation of Delaware Filed May 19,1960, Ser. No. 30,184 Claims. (Cl. 179-1155) This invention relates tosound reproducers for changing electrical oscillations into sound wavesor what are more popularly known as loud speakers.

In certain radio installations space requirements are a very importantfactor. At present this is true particularly in automotive installationswhere total space available for radio equipment is a determining factorin engineering a set and also in determining the shape of the same. Mostrecent automotive receiving equipments consists of at least two units,one of which is a speaker unit. In order to mount the speaker unit innarrow, restricted areas it is necessary to design and build the same ascompactly as possible.

Conventionally cone speakers are built with the magnet structure mountedat the apex of the cone on the outside of the speaker basket so that itsdimension adds to the total depth of the unit. It is possible to mountthe magnct structure for the speaker in the apex of the cone and suchtype of speaker is known as an inverted speaker. In these speakersadvantage is taken of locating the magnet structure inside the cone andthis reduces the depth dimension by the length of the magnet. However,cating the magnet structure in the apex of the cone diaphragm masks thecentral portion of the diaphragm and effects the emanation of soundwaves therefrom to alter the tone. If the magnet structure isminiaturized in an effort to reduce this masking effect and minimizetone impairment then the speaker is not as sensitive to electricaloscillations as it was for sound reproduction.

It is, therefore, an object in making this invention to provide aninverted speaker construction having only slight tone impairment withpractically no loss of sensitivity.

l t is a further object in making this invention to provide an invertedspeaker construction utilizing the same sensitivity as a conventionalspeaker of the same size with a minimum of tone impairment.

It is a still further object in making this invention to provide aninverted speaker construction in which a portion of the magnet structureis mounted within the cone diaphragm to reduce the overall depthdimension.

With these and other objects in view which will become apparent as thespecification proceeds, my invention will be best understood byreference to the following specification and claims and theillustrations in the accompanying drawings, in which:

FIGURE 1 is a side view of a speaker embodying my invention, parts beingbroken away and shown in section;

FIG. 2 is a rear view of the speaker taken on line 22 of FIG. 1;

FIG. 3 is a sectional view taken on line 3-3 of P16. 1;

FIG. 4 is a sectional view taken on line 4-4 of FIG. 2; and,

FIG. 5 is an exploded view of the magnet and immediately associatedparts to show assembly.

Referring now more particularly to the drawings, there is shown thereina metal speaker basket 2 of conical shape within which the speaker cone4 is to be mounted. The outer elliptical periphery of the speaker cone 4is corrugated as shown at 6 so that the speaker may be moved axiallywith a piston-like movement to properly reproduce audible sound waves.The rim 8 of the speaker cone is adapted to be firmly attached to theflanged rim 10 of the speaker basket by any suitable means such asadhesive material. When mounting the speaker in place a flexibleperipheral gasket 12 is fitted within the flanged edge 10 to sealagainst a frame and spaces the speaker diaphragm from porous facingmaterial 15 which protects the front of the speaker and gives it anattractive appearance. This is conventional speaker construction andforms no part of the present invention.

As earlier mentioned the majority of the present speakers have themagnet structure mounted beyond the apex of the cone and outside thebase of the speaker basket.

In the present instance, however, in order to conserve space it isproposed to mount a portion of the magnet structure within the cone inorder to lessen the total depth of the speaker structure. In this casethe magnet structure consists of a permanent magnet 14, a front polepiece 16, a real pole plate 18, a front pole plate together withsuitable spacers 22 and securing bolts 24 and 26. The parts are perhapsbest individually shown in the exploded view in FIG. 5. In assemblingthe parts together a subassembly is first made of the magnet 14, polepiece 16 and pole plate 18 by first soldering the magnet to the poleplate 18 and then the pole piece 16 to the front surface of the magnet.Once these parts are in place the spacers 22 can be secured to the poleplate 18 by inserting and tightening the cap screws 26.

The central portion of the conical diaphragm 4 has a central openingtherein in which is secured a cylindrical member 28 whose axis iscoincident with that of the cone and which extends back into the cone tosupport at its innermost end the voice coil 31'). The diameter of thecylinder 28 is sutficient to slide over the magnet 14 and pole piece 16so that the voice coil when in place will lie around the periphery ofthe circular pole piece 16 as shown in FIG. 4. The basket 2 has arelatively fiat inner end as shown at 32 having a central opening 34therein through which the magnet 14 projects when the subassembly,consisting of the magnet 14, pole piece 16, pole plate 18 and spacers,is placed in position. The pole plate 18 is firmly secured to the outerface 32 by any suitable mechanical means such as staking, soldering,etc. At the inner end of the diaphragm 4 and surrounding the cylindricalsupporting member 28 is a corrugated supporting spider member 36 whichis secured to the diaphragm at its inner periphery and also cemented tothe inside of the end of the basket 32 around its outer periphery asshown at 38.

In assembling this structure the subassembly of the pole plate 18,magnet 14 and pole piece 16 may be firmly se cured to the outer end ofthe basket with the spacers 22 extending through notches 23 provided inthe basket, and notches in the edge of the spider 36. The diaphragm isthen inserted into the basket with the cylindrical member 28 fitted downover the magnet 14 and pole piece 16 and the spacers 22 projectingthrough holes 27. The corrugated supporting member 36 is then cementedto the inner end of the basket. As the cylindrical member 28 is fittedover the magnet 14 and pole piece 16, and the spacers 22 are located andfitted through openings 27 in the diaphragm, the assembly nearscompletion. The openings 27 are of sufiicient size so that they easilyclear the outer surface of the spacers and will not rub thereagainst.When these members are all in place the front pole plate 20 is placed inposition around the outer periphery of the voice coil '30 so that thecentral opening 42 therein is equally spaced on all sides. The capscrews 24 are threaded down into the mating threaded openings in thespacers 22 and the assembly tightened. Lastly, of course, the outerperiphery 8 of the diaphragm 4 is secured to the flange 10 and gasket 12and fabric or other decorative or protective member 15 is cemented tothe front of the speaker.

The magnetic structure consisting of magnet 14, rear pole plate 18, rearcap screws 26, spacers 22, front pole plate 20, front cap screws 24, andpole piece 16 functions as a unit. Each of the plates, spacers andscrews must be designed of good magnetic material and of suflicientcross-sectional area to provide a low reluctance path for the magneticlines of force produced by magnet 14. Thus, it is seen that spacers 22not only locate front pole plate 20 with respect to rear pole plate 13but also they provide a low reluctance magnetic path between the twoplates.

It will be seen that with this construction the majority of the magnetstructure is located within an area from the apex of the cone inward andthat the magnet structure does not increase the overall depth of thespeaker structure to any extent and further that the magnet structurehas not been miniaturized or made smaller than usual so that thesensitivity of the speaker has not been reduced and yet it does notmaterially mask the diaphragm to prevent its tonal reproduction.

What is claimed is:

l. In an electro-acoustic transducer, a conical shaped frame having anannular peripheral section and a reduced planar apical section parallelto the plane of the annular peripheral section, a conical diaphragmmember of similar configuration to the frame and having annular flexiblesupporting portions secured to said frame at both the annular peripheralsection and the apical section to support said diaphragm member foraxial movement, a hollow cylindrical member secured to and extendingthrough the apical section of the diaphragm member on its axis, a voicecoil supported on said cylindrical member inside the conical diaphragmmember, a short cylindrical permanent magnet supported on the planarapical section of the frame and extending inside the cylindrical member,a pole piece mounted on the inner end of the permanent magnet andlocated within the voice coil and a pole plate having a central openingtherein of larger diameter than the voice coil mounted in planaralignment with the pole piece and supported solely by means extending tothe apical section of the frame to provide an air gap for the voice coilwith the pole piece.

2. in an electro-acoustic transducer having a conical frame and aconical diaphragm supported therein for axial movement to reproduceaudible sounds, said diaphragm and frame having matching centralopenings therein at the juxtapositioned apical ends of each, acylindrical magnetic assembly including a permanent magnet and polepieces mounted on the face of the frame adjacent the apical openings andextending through the openings to a position within said conicaldiaphragm, a cylindrical member mounted on said diaphragm surroundingthe magnet assembly, a voice coil mounted on said cylindrical member inalignment with one of the pole pieces, and a pole plate having a centralopening therein supported entirely by said frame mounted in planaralignment with the voice coil and forming an air gap with said polepiece within which said voice coil may lie.

3. In an electro-acoustic transducer having a conical frame and asimilarly shaped flexible diaphragm mounted therein for axial movementto reproduce audible sounds, said diaphragm having a central axialopening therein at its apical end, a magnet assembly including apermanent magnet and pole pieces mounted in the apical end of the frameand extending into the flexible diaphragm through the central opening, apole plate carried by the apical end of the frame and having an openingtherein lying in planar relation with the inner end of the magnetassembly and forming an annular air gap therewith and a voice coilsupported by the diaphragm in the annular air gap so formed to drive thediaphragm.

4. In an clectro-acoustic transducer having a conical frame and asimilarly shaped flexible diaphragm mounted therein for axial movementto reproduce audible sounds, said diaphragm having a central axialopening therein at its apical end, a magnet assembly including apermanent magnet and pole pieces mounted on the apical end of the frameand extending into the flexible diaphragm through the central opening, apole plate carried by the apical end of the frame and having an openingtherein lying in planar relation with the inner end of the magnetassembly, and forming an annular air gap therewith, a cylindrical sleevecarried by the inner end of the flexible diaphragm and enclosing themagnet assembly but of sufficient inner diameter to be spaced therefromand also of insufficient outside diameter to engage the surface of theopening in the pole plate and a voice coil carried by the cylindricalsleeve in the annular air gap to drive the diaphragm.

5. In an electro-acoustic transducer having a conical frame and asimilarly shaped flexible diaphragm mounted therein for axial movementto reproduce audible sounds, said diaphragm having a central axialopening therein at its apical end, a magnet assembly including apermanent magnet and pole pieces mounted on the apical end of the frameand extending into the flexible diaphragm through the central opening, acylindrical sleeve carried by the inner end of the flexible diaphragmsurrounding but in spaced relation to the magnet assembly, supportingmeans carried by the apical end of the frame adjacent the magnetassembly and extending through openings in the flexible diaphragm, apole plate mounted on said supporting means having a central openingtherein to fit over the inner end of the magnet assembly and mounted inplanar relation therewith to provide an annular air gap in which thecylindrical sleeve is positioned and a voice coil carried by said sleevein said annular gap to drive the diaphragm.

References Cited in the file of this patent UNITED STATES PATENTS2,537,723 Ward Jan. 9, 1951 FOREIGN PATENTS 983,550 France Feb. 14, 19511,086,050 France Aug. 4, 1954

